I can see why you all are taken a'back by the age gap between the two, but in those time back then, this was the norm, so I dont really see a problem, when it's just 8 years apart, and because this whole thing is fiction.
On the other hand, if this was in a realistic setting then yes, that's a'tad gross.
But she is mentally 20, while physically being 16... idk 🤷♀️